1. Field of the Invention
Aspects of the present invention relate to a surface-treated electrode active material, a method of surface treating an electrode active material, and an electrode and a lithium secondary battery including the electrode active material, and more particularly, to a surface-treated electrode active material including a surface metal oxide layer having higher degree of reduction of metal than a bulk metal oxide layer, a method of surface treating an electrode active material, an electrode including the surface-treated electrode active material, and a lithium secondary battery including the electrode.
2. Description of the Related Art
Lithium secondary batteries have been used as power supply sources of many mobile devices due to their high energy densities and easy designs. Recently, as lithium secondary batteries are used as power supply sources for electric cars and for power storage devices in addition to portable information technology (IT) devices, studies on materials having high energy densities and long lifetimes have increased. Here, coating a material on a surface of an electrode active material is an effective method of improving performance by modifying the electrode active material with a relatively simple process by using a well-known electrode active material.
Various methods of coating an inorganic material on a surface of an electrode active material are known to improve the performance of a battery. Examples of the inorganic material include metal oxides and fluorides, such as aluminum oxide (Al2O3), magnesium oxide (MgO), zinc oxide (ZnO), aluminum fluoride (AlF3), zinc fluoride (ZnF2), and magnesium fluoride (MgF2).
Coating a material on the surface of the electrode active material largely has two effects: preventing of a side reaction generated due to electron transfer as an electrolyte directly contacts the surface of the electrode active material and removing of by-products that are generated during charging and discharging of a battery that degrades cell performance.
As requirements for high energy density have increased recently, studies on an electrode active material for high voltage are being performed. However, additional studies are required to develop a coating material that suppresses oxidation of an electrolyte on a surface of the electrode active material, where the oxidation is inevitably generated under high voltage conditions. Also, unlike batteries for mobile devices, batteries for electric cars and power storage devices need to operate and be stored in places where the external temperature is high, and the temperature thereof may easily increase due to instant charging and discharging. Accordingly, such batteries need to satisfactorily operate and store energy even at a high temperature.